Conventionally, ceramic electronic components have been known which include a magnetic section, and an internal conductor buried in the magnetic section. The magnetic section and internal conductor are preferably subjected to co-firing in the interest of expediting the manufacturing process. Further, to save cost, the development of internal conductors containing Cu as their main constituent has been advanced. As such electronic components, copper conductor co-fired ferrite elements are known, for example, as in Japanese Patent Application Laid-Open No. 7-97525.
In this Japanese Patent Application Laid-Open No. 7-97525, the addition of low-melting-point glass components of PbO, B2O3, and SiO2 to a Ni—Zn ferrite material allows firing at low temperatures of 950 to 1030° C. under a nitrogen atmosphere, and allows co-firing with Cu.
On the other hand, the Ellingham diagram shown in E. T. T. Ellingham: J. Soc. Chem. Ind., UK, vol. 63, p. 125, 1944 is known as indicating the equilibrium oxygen partial pressures for oxides. According to this Ellingham diagram, it is known that from the relationship between the equilibrium oxygen partial pressure of Cu—Cu2O and the equilibrium oxygen partial pressure of Fe2O3—Fe3O4, there is no region where Cu and Fe2O3 coexist at 800° C. or higher. More specifically, at temperatures of 800° C. or higher, when firing is carried out with the oxygen partial pressure set in such an atmosphere that maintains the state of Fe2O3, Cu is also oxidized to produce Cu2O. On the other hand, when firing is carried out with the oxygen partial pressure set in an atmosphere that does not oxidize Cu, Fe2O3 is reduced to produce Fe3O4.